So, if you had a jittery signal that you wanted to be constant and noise-free, are there ICs that you could attach to reduce the noise before the signal is outputted to a device?
1. Jittery as in, you expect 5 volts but get random voltages between like 4.8 and 5.2 or something. Ya know, noisy.Couple of questions:
In general noise can be reduced or attenuated, but it cannot be eliminated -- sorry.
- What kind of "jittery signal" are you talking about?
- What do you mean by "constant"?
- What kind of device is the signal going to?
In fact, CD4000B series devices excel at eating noise in cases likes this.I would try sending the signal through a buffer (7404, 7414, or something like that) and heavily filter the power supply to that chip to remove the noise.
What do you mean, how do I filter the power?and heavily filter the power supply to that chip
The reason I asked is that "jitter" usually refers to changes in phase or frequency of a signal. If you are talking about a digital signal going to a speaker it is going to sound like crap regardless of what you do. Have you actually observed the "jitter" you spoke of on an oscilloscope? 400 mV peak to peak seems unusual for a signal that normally goes between +5V and GND. Using a CMOS buffer may help you, but haphazard layout and grounding just might introduce additional problems. In my experience digital signals are hardly ever constant and in most case it doesn't matter since only the logic thresholds are important for digital purposes. It might be possible to use some RC filtering to round off the square edges of your digital signal going to the speaker, but that is about the best you can hope for.1. Jittery as in, you expect 5 volts but get random voltages between like 4.8 and 5.2 or something. Ya know, noisy.
2. Constant as in, you expect 5 volts and get 5 volts.
3. In my case, a speaker, but it could be anything.
I want to send an oscillating signal out the joystick port of my Commodore 64, by writing 0 and 1 to the bits in the register that corresponds with the port. The problem is that the port is a little noisy, so it doesn't sound that great.
I see. I plan on getting a DAC so that I can experiment with different waveforms (aside from square waves). I was really just messing around with this pure digital thing, my end goal is to make a programmable waveform generator. Now that I think of it though, wouldn't a DAC get rid of some of the noise? If I send a somewhat noisy digital signal in, it'd still produce a constant voltage, right?The reason I asked is that "jitter" usually refers to changes in phase or frequency of a signal. If you are talking about a digital signal going to a speaker it is going to sound like crap regardless of what you do. Have you actually observed the "jitter" you spoke of on an oscilloscope? 400 mV peak to peak seems unusual for a signal that normally goes between +5V and GND. Using a CMOS buffer may help you, but haphazard layout and grounding just might introduce additional problems. In my experience digital signals are hardly ever constant and in most case it doesn't matter since only the logic thresholds are important for digital purposes. It might be possible to use some RC filtering to round off the square edges of your digital signal going to the speaker, but that is about the best you can hope for.
Oh, ok. Interesting read, thanks.
Good point, I never thought about that. That's why I should use a DAC.In my experience digital signals are hardly ever constant and in most case it doesn't matter since only the logic thresholds are important for digital purposes.
Most likely a commerical DAC chip would not use the input digital signals to directly derive the analog output levels.I see. I plan on getting a DAC so that I can experiment with different waveforms (aside from square waves). I was really just messing around with this pure digital thing, my end goal is to make a programmable waveform generator. Now that I think of it though, wouldn't a DAC get rid of some of the noise? If I send a somewhat noisy digital signal in, it'd still produce a constant voltage, right?
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It's a crude illustration, but you can see that even though the digital "1s" aren't always represented with exactly 5v (because of noise), it's close enough that you still end up with a stable output. So by "filtering" through the DAC, I could probably significantly reduce the noise and get a much cleaner square wave (and be able to make other waveforms as well).
Power supplies can be noisy. Especially if there are load transients which will happen when digital logic IC's are powered by the power supply. You need to get an oscilloscope and start poking around in circuits so you have some idea of what to expect.So it looks like the voltages of the inputs would directly effect the output of a resistor ladder. But, instead of sending the digital signal directly to the DAC, I thought I could send it to the bases of some transistors. The collectors would go to VCC, and the emitters to the DAC. Since VCC is constant (no noise) this would filter the noise out right? Because the noisy signal is just used to activate the transistors (being used as switches) not actually to create the analog output.
Does this sound ok?
Typically, a DAC uses a low-noise stable voltage reference from which to derive it's output.So it looks like the voltages of the inputs would directly effect the output of a resistor ladder. But, instead of sending the digital signal directly to the DAC, I thought I could send it to the bases of some transistors. The collectors would go to VCC, and the emitters to the DAC. Since VCC is constant (no noise) this would filter the noise out right? Because the noisy signal is just used to activate the transistors (being used as switches) not actually to create the analog output.
Does this sound ok?
5 bits, and as little as possible!Typically, a DAC uses a low-noise stable voltage reference from which to derive it's output.
How many bits do you require, and how much noise are you willing to deal with?
This is not an appropriate specification. "As little as possible" is out of your price range.5 bits, and as little as possible!
I'm only 15 so I don't have a job. I have $40 to my name lol. What's the cheapest scope I can get?Power supplies can be noisy. Especially if there are load transients which will happen when digital logic IC's are powered by the power supply. You need to get an oscilloscope and start poking around in circuits so you have some idea of what to expect.
by Duane Benson
by Jake Hertz
by Duane Benson